数据中心用泵驱动两相冷却回路换热特性研究

发布时间：2018-01-09 11:00

本文关键词：数据中心用泵驱动两相冷却回路换热特性研究　出处：《北京工业大学》2015年博士论文　论文类型：学位论文

【摘要】：能源问题是现代社会发展的三大基本问题之一。随着大数据时代的到来,数据中心数量和能耗迅速上升,其中空调能耗占总能耗40%左右。在过渡季节和冬季,可利用室外自然冷源对数据中心进行冷却,降低空调能耗。本文设计一种泵驱动两相回路换热装置用于数据中心自然冷却,通过仿真和试验对其换热特性进行了深入研究,主要内容包括:基于工质在蒸发器出口和冷凝器进口状态,归纳出四种循环模式,过热循环、两相循环、过冷-两相循环和过冷循环,通过理论和试验发现两相循环为最佳模式。利用传热和压降方程建立泵驱动两相回路的一维稳态数学模型,并分析了各段阻力对系统循环和换热的影响。随着蒸发器进口到储液罐进口的工质流动阻力增加,蒸发器进口工质过冷度升高;随着冷凝器出口到储液罐进口的阻力增加,蒸发器进口和冷凝器出口的工质过冷度均升高;随着蒸发器或冷凝器阻力的增大,换热量先升高后降低。蒸发器与冷凝器连接管和冷凝器出口到储液罐进口连接管阻力增大,两器总换热量逐渐降低,前者阻力对应的换热衰减率大于后者。在蒸发器内,工质温度先升高后降低,当工质达到饱和液时,蒸发器内出现温差窄点和换热窄点。蒸发器的换热量分布主要集中在换热器的进口段和出口段。在冷凝器内,工质温度逐渐降低,冷凝器内微元换热量逐渐降低。当工质达到饱和液时,冷凝器出现温差拐点和换热拐点。通过分析表明,蒸发器与冷凝器结构和运行条件相同时,单回路纯工质的泵驱动极限温度效率为50%。基于温差均匀性原理,提出一种多回路泵驱动两相回路换热装置,推导出换热装置的总温度效率与回路数和单回路温度效率的计算公式。单回路效率高时,回路数选择较少为宜,单回路效率低时,回路数选择较多为宜。通过试验研究,分析了泵驱动两相回路的流量特性和换热特性。在不同换热温差下,随着流量的增大,换热量均是先增加后降低再升高。随着换热器台数的同步增加,换热量和温度效率增加逐渐变缓,换热器均为1台时,换热量为2.61kW,温度效率为22.18%,两器均为3和6台时,换热量分别为4.19 kW和4.43 kW,温度效率分别为34.89%和37.81%。分析每个换热器进出口工质和水温度发现,蒸发器内存在温差和换热窄点,蒸发器的换热量主要在首尾两台换热器,中间换热器的换热量占总换热量较小。在理论和试验基础上,搭建了数据中心用泵驱动两相回路换热装置,试验结果表明:在10°C温差下,换热装置的换热量为12.47kW,COP为3.75,25°C温差时,换热量为31.17kW,COP为9.37。分析流量和阻力特性得出,蒸发器出口工质干度在0.3至0.6的范围时换热量变化不显著,较为适宜。随着室外温度变化,机组换热量与室内外温差成线性关系。通过分析其换热特性、流量特性和室内外换热温差特性,提出换热装置应用于数据中心自然冷却的控制策略。
[Abstract]:The energy problem is one of the three basic problems of the development of modern society. With the advent of the era of big data, and the number of data center energy consumption increased rapidly, the air conditioning energy consumption accounted for about 40% of total energy consumption. In the transition season and winter, can use outdoor natural cold source of the data center cooling, reducing the energy consumption. This paper designs a pumped two-phase heat transfer device used for data center cooling, through simulation and experiments on the heat transfer characteristics are studied, the main contents include: the refrigerant in the evaporator outlet and inlet of the condenser based on the state, summed up the four kinds of circulation patterns, superheat cycle, two-phase cycle, cold and cold - two-phase cycle cycle through the theory and experiment found that two-phase cycle is the best model. The one-dimensional steady-state mathematical model is established using pumped two-phase heat transfer and pressure drop equation, and analyzes the period of resistance on the system Effect of circulation and heat transfer. With the increase of refrigerant flow resistance of evaporator inlet to the reservoir inlet, evaporator inlet subcooling degree increased with the increase of export to the condenser; the liquid storage tank inlet resistance, refrigerant evaporator inlet and outlet of the condenser undercooling were increased; with the increase of resistance of evaporator or condenser heat transfer, first increased and then decreased. The evaporator and the condenser connecting pipe and condenser outlet to the reservoir inlet connection pipe resistance increases, two for the total heat transfer rate decreased gradually, the heat transfer rate of attenuation is larger than the latter. The corresponding resistance in the evaporator, refrigerant temperature increased first and then decreased, when the saturated liquid refrigerant when the evaporator temperature and heat pinch pinch. Heat distribution mainly concentrated in the inlet and outlet section of the heat exchanger evaporator. The condenser, refrigerant temperature gradually decreased, the condenser heat transfer in micro element Decreased gradually. When the working fluid saturated liquid, condenser temperature and heat transfer through the inflection point inflection point. Analysis shows that the evaporator and the condenser structure and operation conditions, the single loop of pure refrigerant pump drive limit temperature efficiency of 50%. temperature uniformity is proposed based on the principle of two-phase loop of a multi loop heat pump device efficiency formula and loop temperature heat exchanger is deduced and the number of single loop temperature efficiency. High efficiency single loop, loop number less suitable for single loop low efficiency, large number of loop selection is appropriate. Through experimental research, analysis of the flow characteristics of the pump driven two-phase loop and change thermal characteristics. In different heat transfer temperature difference, along with the increase of flow rate, the heat transfer is increased first and then decreased and then increased. With the increase of heat exchanger units, heat transfer and temperature efficiency increased gradually slow, heat exchangers are 1, heat 2.61kW, temperature efficiency of 22.18% and two are 3 and 6, the heat transfer were 4.19 kW and 4.43 kW, the temperature efficiency were 34.89% and 37.81%. analysis of each heat exchanger inlet and outlet refrigerant and water temperature, evaporator temperature and heat transfer in memory to narrow the heat transfer in the evaporator, the main and two heat exchangers, intermediate heat exchanger heat total heat exchanger is small. Based on the theory and experiment, build a data center with a pump driven two-phase loop heat exchanger, experimental results show that the temperature difference of 10 C, the amount of heat exchanger heat exchanger for 12.47kW, COP for 3.75,25 ~ C temperature, heat transfer for the 31.17kW, COP and 9.37. analysis in order to obtain the flow resistance characteristics, the outlet of the evaporator refrigerant dryness in the range of 0.3 to 0.6 of the heat did not change significantly, more suitable. With the outdoor temperature changes, unit heat transfer and the indoor temperature is linear By analyzing the characteristics of heat transfer, flow rate and temperature difference between indoor and outdoor heat transfer, the control strategy for the application of heat exchanger to the natural cooling of the data center is put forward.

【学位授予单位】：北京工业大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TK124;TP308

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